This invention relates to colored polycarbonate-polyester compositions having improved weathering properties and process for their formation.
Polyester resins derived from terephthalic acid and reactive derivatives thereof, such as dimethyl terephthalate, and alkanediols have been known for some time and have become important constituents for moldable compositions. Workpieces molded from such polyester resin compositions, alone, or combined with reinforcements, offer a high degree of surface hardness, solvent resistance, abrasion resistance, and high gloss. More recently, blends of such polyester resins with one or more second resins have become of significant commercial interest because such second resins, carefully selected, can greatly improve impact strength, as well as tensile strength, modulus, dimensional stability and distortion temperature under load in parts molded from such compositions. Such second resins can comprise aromatic polycarbonate resins as described for example, in Kawase et al, U.S. Pat. No. 3,953,539 and related polyester-carbonate and polyarylate resins.
Polyester-Polycarbonate blends, like most other plastics, are typically colored with carbon black and titanium dioxide used alone, in combination or with other colorants to produce a range of resins and articles made color. Both titanium dioxide and carbon black are present in such blends as discrete particles. Such typically colored polycarbonate/polyester blends tend to develop haze and surface roughness when subjected to weathering, i.e. either accelerated artificial weathering or natural outdoor weather. This surface roughness shows up as a loss of gloss and/or a color shift. This loss of appearance poses a serious problem for aesthetic applications which require retention of a high gloss appearance.
Hence, it is desirable to obtain improved weathering properties from such colored resins so a high gloss appearance can be retained.
The present invention provides a process for identification and preparation of high gloss retention resin molding formulations comprising a polyester resin and a polycarbonate, polyarylate or polyester carbonate resin where the process comprises the steps of selecting a desirable colorant which is stable at molding temperatures in the resin mixture and has desirable color retention properties when subjected to weathering, determining an optimized concentration of the colorant for maximizing gloss retention properties of the selected colorant by performing weathering testing at differing concentrations of the colorant, and optionally determining a suitable gloss retention agent for addition to the formulation.
In a preferred embodiment of the present invention molding compositions will comprise (a) from 10 to 90 weight percent of a polyester resin; (c) from 90 to 10 weight percent of an aromatic polycarbonate, polyarylate, polyester carbonate resin or blend thereof and a colorant or colorants in a sufficient amount to give a desirable coloration with the optional addition of a suitable gloss retention agent or impact modifier.
Synthetic colorants are typically derived from coal tar or petroleum intermediates. Colorants of many distinct types are available for use in plastics and coatings. The Color Index names hundreds of different colorants of many different chemical classes for instance; nitroso, nitro, mono azo, diazo, triazo, polyazo, azoic, stilbene, carotenoid, diphenylmethane, triarylmethane, xanthene, quinoline, acridine, methine, thiazole, indamine, indophenol, azine, oxazine, thiazine, sulfur, lactone, aminoketone, hydroxyketone, anthraquinone, indigloid, phthalocyanine and inorganic pigments. Colorants may be organic or inorganic, being dyes and or pigments. Dyes are colorants that do not normally scatter light but absorb light at some visible wavelength. Dyes are often soluble, at some concentration, in the polymer matrix of a colored article. Pigments are organic or inorganic colorants that are usually present in a matrix as discrete particles, insoluble in the matrix. The designation of a given colorant as pigment or dye is somewhat arbitrary since it will depend on the polymer matrix, colorant concentration, temperature, crystallinity and other factors.
Despite this huge variety of colorants there exists a problem in finding suitable colorants for thermoplastic polyester- polycarbonate blends, especially blends that will be exposed to direct sunlight and outdoor weathering. The colorant must be stable to polymer processing at high temperature, must not chemically degrade the resin matrix, must provide molded articles that have good initial color tone and high gloss and then, most difficult to achieve, retain the color, gloss and properties under weathering. We have found that surprisingly few specific colorants, that we believe must largely be soluble or very finely dispersed in a specific polyester blend matrix, give shaped articles with good as molded color and gloss and retain a significant portion or those properties when weathered under natural or artificial conditions.
It is desirable to select a colorant that exhibits good color and gloss retention when subjected to weathering test. Color shift and gloss should be desirably measured by a standard test so that comparison data may be generated to select a desirable dye colorant. Color shift measurements may be measured using the CieLAB system using L, a, b values to calculate a color shift: delta E, compared to an unweathered control. Surface gloss, often measured as 60xc2x0 gloss values using ASTM D523, can also be monitored as a function of exposure time under normal weathering or in an accelerated weathering apparatus (xe2x80x9cweatherometerxe2x80x9d) to determine resistance of a material to loss of properties due to photo-aging. The weatherometer as referred to in this application was run according to conditions given in the SAE J1960 or ASTM G26 protocols. Details of the weathering tests are discussed in the examples of the invention.
Examples of the invention will have high gloss as molded, that is with a 60xc2x0 gloss of xe2x89xa780%, most preferred with a gloss of xe2x89xa790%, and will show greater than or equal to 50% retention of said initial gloss after 1000 hours of accelerated weathering under ASTM G26 or SAE J1060 test conditions. The preferred compositions of the invention will show xe2x89xa750% retention of initial gloss after 3000 hours ASTM G26 or SAE J1960 accelerated weathering. The most preferred compositions of the invention will show 50% or greater retention of the initial gloss after 5000 hours of ASTM G26 or SAE J1960 accelerated weathering.
In addition to selecting a colorant that exhibits good color retention when subjected to weathering, it is desirable to independently check the colorant for gloss retention by performing separate weathering test at different concentrations of colorant to find the concentration with the desired optimized gloss retention.
Even further enhanced gloss retention may be desirably achieved with additions of a suitable gloss retention agent such as an UV absorber, for example, benzotriazoles. UV absorbers may be used in any effective concentration with ranges of 0.1-2.0 wt.% (based on the whole composition) being most preferred.
Preferred colorants of the invention having good thermal stability on processing and good retention of gloss during weathering of the compositions of the invention are: solvent green 3, solvent green 28, solvent red 52, solvent red 111, solvent red 135, solvent red 169, solvent red 179, solvent red 207, disperse red 22, vat red 41, solvent orange 60, solvent orange 63, solvent violet 13, solvent violet 14, solvent violet 50, pigment blue 29, amino ketone black (KEYSTONE BLACK AN from Keystone Aniline Co.), disperse blue 73, solvent blue 97, solvent blue 101, solvent blue 104, solvent blue 138, pigment yellow 139, disperse yellow 160, solvent yellow 84, solvent yellow 93, solvent yellow 98, solvent yellow 163 and solvent yellow 160:1.
The most preferred colorants having good thermal stability during processing and having both good color and gloss retention during the weathering of the compositions of the invention are: solvent red 135, solvent red 179, amino ketone black, solvent violet 14, solvent violet 36, solvent violet 50, disperse blue 73, solvent yellow 93, and disperse yellow 160.
In addition to the dye, and the optional gloss retention agent, the molding composition will contain a polyester and polycarbonate, polyarylate or polyester carbonate resin. Suitable polyester resins comprise from 10 to 90 weight percent of the composition of the invention. Polyester components include crystalline polyesters such as polyesters derived from an aliphatic or cycloaliphatic diol, or mixtures thereof, containing from 2 to about 12 carbon atoms and at least one aromatic or aliphatic dicarboxylic acid. Preferred polyesters are crystalline thermoplastics derived from an aliphatic diol and an aromatic dicarboxylic acid having repeating units of the following general formula: 
wherein n is an integer of from 2 to 6, and R is a C6-C20 radical comprising a decarboxylated residue derived from a dicarboxylic acid.
Examples of aromatic dicarboxylic acids represented by the dicarboxylated residue R are isophthalic or terephthalic acid, 1,2-di(p-carboxyphenyl)ethane, 4,4xe2x80x2-dicarboxydiphenyl ether, 4,4xe2x80x2 bisbenzoic acid and mixtures thereof. All of these acids contain at least one aromatic nucleus. Acids containing fused rings can also be present, such as in 1,4- 1,5- or 2,6-naphthalenedicarboxylic acids. Aliphatic dicarboxylic acids, especially cyclic dicarboxylic acids or derivatives may be used. The preferred dicarboxylic acids are terephthalic acid, isophthalic acid, cyclohexane dicarboxylic or mixtures thereof.
The most preferred polyesters are poly(ethylene terephthalate) xe2x80x9cPETxe2x80x9d, and poly(butylene terephthalate), xe2x80x9cPBTxe2x80x9d and (polypropylene terephthalate) Also contemplated herein are the above polyesters with minor amounts, e.g., from about 0.5 to about 25 percent by weight, of units derived from aliphatic acids, diamines and/or aliphatic polyols to form copolyesters. The aliphatic polyols include glycols, such as poly(ethylene glycol) and poly(butylene glycol). Such polyesters can be made following the teachings of, for example, U.S. Pat. Nos. 2,465,319 and 3,047,539.
The preferred poly(1,4-butylene terephthalate) resin used in this invention is one obtained by polymerizing a glycol component at least 70 mole %, preferably at least 80 mole %, of which consists of tetramethylene glycol and an acid component at least 70 mole %, preferably at least 80 mole %, of which consists of terephthalic acid, and polyester-forming derivatives therefore.
The polyesters used herein have an intrinsic viscosity of from about 0.4 to about 2.0 dl/g. as measured in a 60:40 phenol/tetrachloroethane mixture or similar solvent at 23-30xc2x0 C. VALOX Registered TM 315 polyester is particularly suitable for this invention. Preferred PBT resins have an intrinsic viscosity of 1.1 to 1.4 dl/g.
Typically polycarbonates are prepared by reacting a dihydric phenol with a carbonate precursor, such as phosgene, a haloformate or a carbonate ester. Generally speaking, such carbonate polymers may be typified as possessing recurring structural units of the formula 
wherein A is a divalent aromatic radical of the dihydric phenol employed in the polymer producing reaction. Preferably, the carbonate polymers used to provide the resinous mixtures of the invention have an intrinsic viscosity (as measured in methylene chloride at 25xc2x0 C.) ranging from about 0.30 to about 1.00 dl/g. The dihydric phenol which may be employed to provide such aromatic carbonate polymers are mononuclear or polynuclear aromatic compounds, containing as functional groups two hydroxy radicals, each of which is attached directly to a carbon atom of an aromatic nucleus. Typical dihydric phenols are: 2,2-bis(4-hydroxyphenyl) propane; hydroquinone; resorcinol; 2,2-bis(4-hydroxyphenyl) pentane; 2,4xe2x80x2-(dihydroxydiphenyl) methane; bis(2 hydroxyphenyl) methane; bis(4-hydroxyphenyl) methane; bis(4-hydroxy-5-nitrophenyl) methane; 1,1-bis(4-hydroxyphenyl) ethane; 3,3-bis(4-hydroxyphenyl) pentane; 2,2-dihydroxydiphenyl; 2,6-dihydroxynaphthalene; bis(4-hydroxydiphenyl)sulfone; bis(3,5-diethyl-4-hydroxyphenyl)sulfone; 2,2-bis(3,5-dimethyl4-hydroxyphenyl)propane; 2,4xe2x80x2-dihydroxydiphenyl sulfone; 5xe2x80x2-chloro-2,4xe2x80x2-dihydroxydiphenyl sulfone; bis-(4hydroxyphenyl)diphenyl sulfone; 4,4xe2x80x2-dihydroxydiphenyl ether; 4,4xe2x80x2-dihydroxy-3,3xe2x80x2-dichlorodiphenyl ether; 4,4-dihydroxy-2,5-dihydroxydiphenyl ether; and the like.
Other dihydric phenols which are also suitable for use in the preparation of the above polycarbonate resins are disclosed in U.S. Pat Nos. 2,999,835; 3,028,365; 3,334,154; and 4,131,575.
These aromatic polycarbonates can be manufactured by known processes, such as, for example and as mentioned above, by reacting a dihydric phenol with a carbonate precursor, such as phosgene, in accordance with methods set forth in the above-cited literature and in U.S. Pat. No. 4,123,436, or by transesterification processes such as are disclosed in U.S. Pat. No. 3,153,008, as well as other processes known to those skilled in the art.
It is also possible to employ two or more different dihydric phenols or a copolymer of a dihydric phenol with a glycol or with a hydroxy- or acid-terminated polyester or with a dibasic acid in the event a carbonate copolymer or interpolymer rather than a homopolymer is desired for use in the preparation of the polycarbonate mixtures of the invention. Branched polycarbonates are also useful, such as are described in U.S. Pat. No. 4,001,184. Also, there can be utilized blends of linear polycarbonate and a branched polycarbonate. Moreover, blends of any of the above materials may be employed in the practice of this invention to provide the aromatic polycarbonate.
These polycarbonates may be branched or linear and generally will have a weight average molecular weight of from about 10,000 to about 200,000, preferably from about 20,000 to about 100,000 as measured by gel permeation chromatography. The polycarbonates of the invention can employ a variety of end groups to improve performance. Bulky mono phenols, such as cumyl phenol, are preferred.
Preferred resins for enhanced weatherability and UV resistance are esters of aromatic dicarboxylic acids and bisphenols known as polyarylates. Polyarylate copolymers, with carbonate linkages in addition to the aryl ester linkages, known as polyester-carbonates, are also preferred. These resins may be used alone or in combination with each other or more preferably in combination with bisphenol polycarbonates. These resins can be prepared in solution or by melt polymerization from aromatic dicarboxylic acids or their ester forming derivatives and bisphenols and their derivatives. Suitable dicarboxylic acids are iso and terephthalic acid, their esters or acid chlorides. A preferred bisphenol is bisphenol A or its diacetate derivative. Polyester carbonates and polyarylates may also contain linkages derived from hydroxy carboxylic acids such as hydroxy benzoic acid. The most preferred polyester carbonate and polyarylates are derived from bisphenol A and mixture of iso- and terephthalic acid and are amorphous resins. U.S. Pat. No. 4,663,421 describes suitable polyarylates and U.S. Pat. Nos. 3,169,121; 4,156,069 and 4,269,731 describe suitable polyester-carbonates. All 4 patents are hereby incorporated by reference. In a preferred embodiment, the polyester-carbonate to polycarbonate ratio or polyarylate to polycarbonate ratio is 90:10 to 10:90% by weight.
Additional resin components may include, an effective amount of any of the known impact modifiers useful for polyesters and polyester blends. These may be added to the compositions by themselves or in combination with the aforementioned aromatic polycarbonates or polyesters. Useful impact modifiers generally comprise an acrylic or methacrylic grafted polymer of a conjugated diene or an acrylate elastomer, alone or co-polymerized with a vinyl aromatic compound. Other grafted polymers are the core-shell polymers of the type available from Rohm and Haas, for example ACRYLOID EXL2691 and ACRYLOID EXL3330. In general these impact modifiers contain units derived from butadiene in combination with a vinyl aromatic compound, acrylate, or akylacrylate ester such as methacrylate. The aforementioned impact modifiers are believed to be disclosed in Fromuth, et al., U.S. Pat. No. 4,180,494; Owens, U.S. Pat. No. 3,808,180; Farnham, et al., U.S. Pat. No. 4,096,202; and Cohen, et al., U.S. Pat. No. 4,260,693, all incorporated herein by reference. The impact modifier may comprise a two stage polymer having either a butadiene or n-butyl acrylate based rubbery core and a second stage polymerized from methylmethacrylate alone or in combination with styrene. Also present in the first stage are cross linking monomers and graft linking monomers. Examples of the cross linking monomers include 1,3-butylene diacrylate, divinyl benzene and butylene dimethacrylate. Examples of graft linking monomers are allyl acrylate, allyl methacrylate and diallyl maleate.
Additional preferred impact modifiers are of the type disclosed in U.S. Pat. No. 4,292,233, incorporated by reference. These impact modifiers comprise, generally, a relatively high content of a partially cross-linked butadiene polymer grafted base having grafted thereon acrylonitrile and styrene copolymers.
The most preferred impact modifiers are polyolefin copolymers with vinyl epoxide derived units. Such epoxide functional copolymers may be prepared from an olefin, such as ethylene and glycidyl acrylate or methacrylate. Other non functionalized vinyl containing monomers may also be incorporated such as alkyl acrylate or methacrylate, vinyl esters and vinyl ethers. Suitable epoxy containing polyolefin copolymers and terpolymers are described in U.S. Pat. No. 5,907,026 (herein incorporated by reference). The most preferred impact modifiers are ethylene-alkyl methacrylate-glycidyl methacrylate (EMA-GMA) terpolymers. Such epoxy olefin impact modifiers are preferred to be used at 1 to 5% loading.
As previously mentioned the UV resistance and weathering performance of the blends of the invention can be enhanced by addition of ultraviolet radiation absorbers. Benzotriazole UV absorbers are preferred for instance commercially available TINUVIN 234, MIXXIM BB/200 and CYASORB 5411. Other suitable UV absorbers are described in U.S. Pat. No. 5,907,026 hereby incorporated by reference. UV absorbers are used at any effective concentration generally from 0.1-2.0 wt. % of the entire mixture.
When combining polycarbonate, polyarylates or polyester-carbonates with polyester resins it is very desirable to use special stabilizers, often referred to as quenchers, to suppress polycarbonate polyester reaction. These stabilizers are used at a level of 0.01-10 weight percent and preferably at a level of from 0.05-2.0 weight percent. The stabilizers include an effective amount of an acidic phosphate salt; an acid, alkyl, aryl or mixed phosphite having at least one hydrogen or alkyl group; a suitable metal phosphate salt, preferably a Li, Na, K, Mg, Ca or Zn salt; a phosphorus oxo acid, a metal acid pyrophosphate or a mixture thereof. The suitability of a particular compound for use as a stabilizer and the determination of how much is to be used as a stabilizer may be readily determined by preparing a mixture of the polyester component and the polycarbonate with and without the particular compound and determining the effect on melt viscosity or color stability or the formation of interpolymers. These stabilizers are further described in U.S. Pat. No. 5,441,997 in column 6, line 48 to column 7, line 10. This text is incorporated by reference into the present application.
In order to achieve the full benefits of this invention the type and amount of quencher should be chosen so that the colored resin composition is substantially free of particulates. Organic substituted quenchers like; partially esterified phosphorous acid, an acid, alkyl, aryl or mixed phosphite having at least one hydrogen or alkyl group, phosphoric or phosphorous acids are preferred. Mineral quenchers that will act as a particulate filler in the blend are less preferred but may be acceptable at a low level. Similarly any significant level of a particulate additive such as carbon black or titanium dioxide may be detrimental to gloss retention depending on the severity of the weathering conditions and the nature of the polyester blend matrix. The appropriate level of particles allowed into the blend will depend on the matrix and the length of weathering and can be determined using the process of our invention . Polyester blends of the invention with UV stabilizer and further containing at least some level ( greater than 5% preferred,  greater than 10% more preferred) of polyester-carbonate or polyarylate resins will have the best gloss retaining capability under severe weathering conditions. Such polyester polyarylate or polyester-carbonate blends will better tolerate the presence of low levels of particulates than blends of polyester with just aromatic polycarbonate (for examples Bis Phenol A-PC). In any event the gloss retention of all compositions of the invention will benefit from the absence of particulates.
The blends of the invention comprise less than 5 percent by weight additional ingredients which may be added to contribute to additional desirable properties such as: good mechanical properties, oxidation resistance, good processability, i.e. short molding cycle times, good flow, and easy release from the molding tool. Preferred are antioxidants such as hindered phenols, thioesters, phosphonites and phosphites. Mold release agents, especially low molecular weight polyesters such as pentaerythritol tetrastearate (PETS), are also preferred.
The colorants are incorporated into the resin composition by uniformly mixing into the desired resin composition. It is important that colorants be stable at processing temperatures. In a preferred embodiment, the colorant is stable at  greater than 200xc2x0 C. (392xc2x0 F.). Stability is desired at temperatures on the order of about 500xc2x0 F. (260xc2x0 C.), preferably at 550xc2x0 F. (288xc2x0 C.), and even more preferably 575xc2x0 F. (302xc2x0 C.). Unstable colorants should be avoided. As set forth previously in detail, stable colorants include solvent red 179, solvent red 135, solvent yellow 84, and solvent violet 13. Non preferred colorants will be strongly basic or acidic. Colorants with primary amino, sulfonic acid, or lithium, sodium or potassium carboxylate units should be avoided due to potential unfavorable interactions with the polycarbonate, polyester resins or the quenchers used to suppress the polycarbonate-polyester reaction.
Colorants of the invention should be chosen of such structure and at such concentrations that they remain essentially soluble in the matrix resins for the best retention of gloss during weathering. As discussed previously, while low levels of particulates may be present in the blend best performance is achieved in blends essentially free of organic and especially inorganic particulates.
The method of blending the compositions can be carried out by conventional techniques. One convenient method comprises blending the polyester, polycarbonate, colorants and other ingredients in powder or granular form, extruding the blend and comminuting into pellets or other suitable shapes. The ingredients are combined in any usual manner, e.g., by dry mixing or by mixing in the melted state in an extruder, on a heated mill or in other mixers. Colorants or other portions of the blend may be added to the extruder downstream of the throat feed port.
Although it is not essential, best results are obtained if the ingredients are pre compounded, pelletized and then molded. Pre compounding can be carried out in conventional equipment. For example, after predrying the polyester and polycarbonate resins, the resins may be blended with other ingredients and. melt mixed on a single or twin screw extruder. The ingredients can be added all together or fed in portions into different areas of the melt mixing device. It may be advantageous to pre compound some ingredients of the blend before mixing with the remainder of the blend for example as described in U.S. Pat. No. 5,814,712 hereby incorporated by reference.
In the most preferred case using BPA polycarbonate, a polyester-carbonate and PBT or PET, a generally suitable machine temperature will be from about 240xc2x0 C. to about 300xc2x0 C. The pre-compounded composition can be extruded and cut or chopped into molding compounds, such as conventional granules, pellets, etc. by standard techniques. The compositions can be molded in any equipment conventionally used for thermoplastic compositions. For example, good results will be obtained in an injection molding machine, with conventional cylinder temperatures, e.g., 250xc2x0 C. to 275xc2x0 C., and conventional mold temperatures, e.g., 650 to 90xc2x0 C.